1. Field of the Invention
This invention relates to a coextrusion adapter for an extrusion installation with several extruders and a tool supplied by the extruders for producing a composite coextrusion structure of thermoplastic material, wherein the coextrusion adapter has a central conduit with an end at the inlet side for connecting an extruder and an end at the outlet side for connecting a tool, the coextrusion adapter has at least one coextrusion conduit with an inlet end and an outlet end, a further extruder can be respectively connected to the inlet end and the outlet end terminates downstream of the end at the inlet side of the central conduit in the latter, and adjusting devices are assigned to each outlet end of the at least one coextrusion conduit, which have a plurality of adjusting elements which together extend over the width of the outlet end and which can be adjusted independently of each other by actuating drives so that the inside diameter of the respective transverse section of the outlet end can be changed.
2. Discussion of Related Art
Known coextrusion adapters are used for bringing together molten strands of thermoplastic materials coming from several extruders, for example while producing films, plates and panels. For this purpose, the individual melts of thermoplastic material provided by the extruders are brought together in the coextrusion adapter in the desired layer position and are then conveyed together to the extrusion tool for producing the composite coextrusion structure.
While layering different plastic materials within the coextrusion adapter, such as is often the case in actual use, different properties of the plastic materials, in particular different viscosities, or deviations from the selected material flow-through conditions of the individual extruders, must be compensated.
German Patent Reference DE-OS 37 41 793, which establishes the species, provides adjustment devices at the respective outlet end of the coextrusion conduits, which have a plurality of adjusting elements, which together extend over the width of the outlet end and can be adjusted by actuating drives in such a way that the inside diameter of the respective transverse section of the outlet end can be changed. Thus it is possible to affect the cross-sectional profile of the coextruded layer, which is supplied through the coextrusion conduit to the central circuit and the melt conveyed through it. This takes effect individually differently over the entire width of the coextrusion conduit, so that layer thickness tolerances, material throughput, as well as viscosity differences can be compensated. However, with this known device it is only possible to affect the profile of the melt flow supplied through the coextrusion conduit, while profiling of the melt flow moving in the central conduit, which would be desirable for achieving exact tolerances within the composite coextrusion structure, is not possible.
It is known from German Patent Reference DE 197 57 827 A1 to arrange a multi-layer adapter with separators tapering to a point in the meeting area between the central conduit and the coextrusion conduits, wherein the separators are designed as a multitude of separating plates over the entire width of the coextrusion conduits and can be adjusted independently of each other. Although a simultaneous effect on the thickness profile of the melt flowing inside the central conduits, as well as the melt inflowing through the coextrusion conduit is possible, it is not possible to affect the selected setting from the outside without interrupting the production. Instead, it is necessary to remove the separators having a plurality of separator plates from the multi-layer adapter, to adjust it as desired and then to reinstall it, wherein an interruption of the production occurs in each case. Thus the known device is essentially only suited for model tests, in which it is intended to determine the optimally best possible shape of the separator, and wherein afterwards a solid separator without adjustment possibilities is produced from the model having separator plates and used during production.
It is known from European Patent Reference EP 0 161 812 B1 to provide wing-like separating elements, which are pivotable around a pivot axis extending over a width of the coextrusion conduits, by which a compensation of viscosity and pressure differences can be performed in the individual conduits wherein, however, the separating element is seated pivotably in a free-floating manner, for example it is not intended to provide a desired adjustment by exterior adjusting elements. Because the known separating element extends continuously in one piece over the entire width of the coextrusion conduit, a profiling of the inside diameter which differs over the width of the coextrusion conduit is not possible.